Ion detector and system

ABSTRACT

Apparatus and method for detecting current or potential generated in a liquid sample suitable for use in a chromatography or other liquid sample analytical system. One embodiment is an electrolytic ion transfer device with a signal detector in communication with the electrodes of the transfer device. Another is a combination ion transfer device/electrolyte generator. Another substitutes a detector for the ion transfer device in the combination.

BACKGROUND OF THE INVENTION

The present invention relates to apparatus for detecting current orpotential generated by ionic species in a liquid sample solution.

Conductivity detection is a bulk property detection and the totalconductance depends on the nature of the ions via the charge on the ionand the mobility and the concentration in a sample. The specificconductance of a solution is the sum of the concentration-mobilityproduct of the different ions present. It is well known that equalconcentrations of specific different compounds, e.g. NaCl and HCl, havevastly different specific conductance. Conductivity however responds toall ionic solutes but cannot provide a measure of total charge.

Coulometry is an analytical method for determining an unknownconcentration of an analyte in a sample solution by completelyconverting the analyte from one oxidation state to another. Coulometryis an absolute measurement methodology and requires no calibration.However coulometry is inapplicable for a great variety of ionic speciesanalytes, e.g., Na⁺ or SO₄ ²⁻ whose redox potentials lie beyond a valuewhere solvent breakdown occurs or, e.g., with dilute Cl⁻, where theredox process is not current efficient. There is no known technique thatprovides a measurement of the total charge present in a sample solution.

In ion chromatography, calibration is typically performed by running aresponse versus concentration plot, after analyzing a number ofdilutions of standard samples. To analyze multiple components ofinterest in a sample, each of the multiple components must becalibrated. Multiple standard preparations and calibrations can becumbersome. It would be useful to develop a simpler detectionmethodology for ion chromatography.

In ion chromatography, a particular detection scheme is chosen based onthe properties of the analytes. For example, analysis of nitrate,bromide or iodide can be pursued by ultraviolet detection (UV) sincethese analytes absorb in UV. However other common ions such as fluoride,sulfate, phosphate do not absorb UV and so will not respond to direct UVdetection. It would be useful in ion chromatography analysis totransform the peaks of interest if possible to a different species tofacilitate detection by a chosen detection approach such as UVdetection. Similarly in Mass spectrometry (MS) in the single ionmonitoring (SIM) mode, the MS parameters are optimized to facilitateobservation of a specific mass. This mode provides the highestsensitivity for specific ions or fragments. It would be useful totransform the peaks of interest to a form that could be detected by theMS in the SIM mode.

SUMMARY OF THE INVENTION

In one embodiment, apparatus is provided for detecting current orpotential generated by ionic species in a sample solution containingsuch ions, the apparatus including (a) an electrolytic ion transferdevice including (1) a sample flow-through channel having an inlet andan outlet, (2) a first charged barrier disposed along the sampleflow-through channel in fluid contact therewith, the first chargedbarrier being capable of passing ions of one charge, positive ornegative, and of blocking bulk liquid flow, (3) a first chamber disposedon the opposite side of the first charged barrier from the sampleflow-through channel, and (4) first and second electrodes in electricalcommunication with the first chamber and the sample flow-throughchannel, respectively; and (b) an electrical signal detector inelectrical communication with the first and second electrodes.

In another embodiment, apparatus is provided for detecting ions in asample solution containing such ions, the apparatus including (a) anelectrolytic ion transfer device including (1) a sample flow-throughchannel, (2) a first charged barrier disposed along the sampleflow-through channel in fluid contact therewith, the first chargedbarrier being capable of passing ions of one charge, positive ornegative, and of blocking bulk liquid flow, (3) a first chamber disposedon the opposite side of the first charged barrier from the sampleflow-through channel, and (4) first and second electrodes in electricalcommunication with the first chamber and said sample flow-throughchannel, respectively; and (b) an electrolytic electrolyte generatorincluding (1) a first electrolyte source reservoir, (2) a firstelectrolyte generation chamber, (3) a first electrolyte charged barriercapable of passing ions of one charge, positive or negative, and ofblocking bulk liquid flow, disposed between the first electrolyte sourcereservoir and the first electrolyte generation chamber, and (4) thirdand fourth electrodes in electrical communication with the first andsecond electrodes, respectively, and with the first electrode sourcereservoir and the electrolyte generation chamber, respectively, and (c)a detector for the electrolyte generated in the electrolyte generationchamber in fluid communication therewith.

In another embodiment, apparatus is provided for detecting current orpotential generated by ions in a sample elution including (a)flow-through ion exchange medium in a housing having an inlet and anoutlet, (b) first and second electrodes disposed to pass an electriccurrent through the ion exchange medium, and (c) an electric signaldetector in electrical communication with the first and secondelectrodes.

In another embodiment, a method is provided for detecting current orpotential generated by ions in a sample solution containing such ions,the method including (a) providing an electrolytic ion transfer deviceincluding a sample flow-through channel, a first charged barrier capableof passing ions of one charge, positive or negative, and of blockingbulk liquid flow disposed along the sample channel in fluid contacttherewith, and a first ion receiving chamber disposed on the oppositeside of the first barrier from the sample barrier, (b) flowing anaqueous sample stream including sample ionic species through the samplechannel to exit as a sample channel effluent, (c) passing an electriccurrent between first and second electrodes in electric communicationwith the sample stream in the sample channel and aqueous liquid in theion receiving chamber, respectively, (d) transporting at least a portionof the sample stream ions across the first charged barrier into aqueoussolution in the first ion receiving chamber under the influence of theelectric current, and, (e) detecting an electrical signal produced bycurrent flowing between the first and second electrodes.

In another embodiment, a method is provided for detecting ions in asample solution containing such ions, the method including (a) providingan electrolytic ion transfer device including a flow-through samplechannel, a first charged barrier capable of passing ions of one charge,positive or negative, and of blocking bulk liquid flow disposed alongthe sample channel in fluid contact therewith, and a first ion receivingchamber disposed on the opposite side of the first barrier from thesample barrier, (b) flowing an aqueous sample stream including ionsthrough the flow-through said sample channel, (c) passing an electriccurrent between first and second electrodes in electric communicationwith the sample stream in the sample channel and aqueous liquid in theion receiving chamber, respectively, (d) transporting at least a portionof the sample stream ions across the first charged barrier into aqueoussolution in the first ion receiving chamber under the influence of theelectric current, (e) providing an electrolytic electrolyte generatorcomprising a first electrolyte source reservoir separated from anelectrolyte generating chamber by a second charged barrier havingexchangeable ions capable of passing ions of one charge, positive ornegative, (f) flowing an aqueous solution through the electrolytegenerating chamber, (g) passing current flowing between the first andsecond electrodes to third and fourth electrodes, respectively, inelectrical communication with solution in the first electrolyte sourcereservoir and in the first electrolyte generating chamber, respectively,to pass ions of one charge, positive or negative, through the secondcharged barrier to generate electrolyte aqueous solution in the firstelectrolyte generation chamber, and (h) detecting the generatedelectrolyte solution.

In another embodiment, a method is provided for detecting current orpotential generated by sample ionic species in a sample solutionincluding (a) flowing a sample solution including sample ionic speciesthrough ion exchange medium, (b) passing an electric current through theion exchange medium between first and second electrodes, and (c)detecting an electric signal produced by current flowing between thefirst and second electrodes. In another embodiment, apparatus isprovided for detecting analyte in a sample solution containing theanalyte. The apparatus includes (a) a detector sample flow channel forliquid sample containing analyte, (b) a signal detector operativelyassociated with the detector sample flow channel for detecting analytein liquid sample therein, the signal detector generating an electricalsignal in response to the concentration of the analyte, (c) anelectrolytic electrolyte generator including (1) a first electrolytesource reservoir, (2) a first electrolyte generation chamber, (3) afirst electrolyte charged barrier capable of passing ions of one charge,positive or negative, and of blocking bulk liquid flow, disposed betweenthe first electrolyte source reservoir and the first electrolytegeneration chamber, and (4) first and second electrodes in an electricalcircuit with electrical communication with the detector generatedelectric signal, and with the first electrode source reservoir and theelectrolyte generation chamber, respectively, and (d) an electrolytedetector for the electrolyte generated in the electrolyte generationchamber in fluid communication therewith.

In another embodiment, a method is provided for detecting ions in asample solution containing such ions. The method includes (a) flowing anaqueous sample stream including analyte through a detector sample flowchannel, (b) detecting the concentration of analyte in the sample flowchannel and generating an electrical signal in response to the detectedconcentration of the analyte, (c) providing an electrolytic electrolytegenerator comprising a first electrolyte source reservoir separated froman electrolyte generating chamber by a second charged barrier havingexchangeable ions capable of passing ions of one charge, positive ornegative, (d) flowing an aqueous solution through the electrolytegenerating chamber, (e) passing the generated electrical signal acrossto first and second electrodes of opposite polarity, in electricalcommunication with solution in the first electrolyte source reservoirand in the first electrolyte generating chamber, respectively, to passions of one charge, positive or negative, through the second chargedbarrier to generate electrolyte aqueous solution in the firstelectrolyte generation chamber, and (f) detecting the generatedelectrolyte solution.

In another embodiment, apparatus is provided for detecting ions in asample solution containing such ions. The apparatus includes (a) anelectrolytic ion transfer device including (1) a sample flow-throughchannel, (2) a first charged barrier disposed along the sampleflow-through channel in fluid contact therewith, the first chargedbarrier being capable of passing ions of one charge, positive ornegative, and of blocking bulk liquid flow, (3) a first chamber disposedon the opposite side of the first charged barrier from the sampleflow-through channel, and (4) first and second electrodes in electricalcommunication with the first chamber and said sample flow-throughchannel, respectively; (b) an electrolytic electrolyte generator havingan inlet and an outlet and having third and fourth electrodes inelectrical communication with the first and second electrodes,respectively, and (c) a detector in fluid communication with theelectrolyte generator outlet.

In another embodiment, apparatus is provided for detecting ions in asample solution containing such ions. The apparatus includes (a) anelectrolytic ion transfer device including (1) a sample flow-throughchannel, (2) a first charged barrier disposed along the sampleflow-through channel in fluid contact therewith, the first chargedbarrier being capable of passing ions of one charge, positive ornegative, and of blocking bulk liquid flow, (3) a first chamber disposedon the opposite side of the first charged barrier from the sampleflow-through channel, and (4) first and second electrodes in electricalcommunication with the first chamber and the sample flow-throughchannel, respectively; and (b) an electrolytic electrolyte generatorcomprising: (1) flow-through ion exchange medium, having an inlet and anoutlet, (2) third and fourth electrodes in electrical communication withthe first and second electrodes, respectively, and with the ion exchangemedium, and (c) a detector in fluid communication with the ion exchangemedium outlet.

In another embodiment, apparatus is provided for detecting analyte in asample solution containing said analyte. The apparatus includes (a) adetector sample flow channel for liquid sample containing analyte, (b) asignal detector operatively associated with the detector sample flowchannel for detecting analyte in liquid sample therein, the signaldetector generating an electrical signal in response to theconcentration of the analyte, (c) an electrolytic electrolyte generatorcomprising flow-through ion exchange medium having an inlet and anoutlet, and first and second spaced-apart electrodes disposed adjacentthe ion exchange medium to pass an electrical potential through themedium, the first and second electrodes being in electricalcommunication with the detector generated electrical signal, and (d) anelectrolyte detector in fluid communication with the ion exchange mediumoutlet.

In another embodiment, a method is provided for detecting ions in asample solution containing such ions. The method includes (a) flowing anaqueous sample stream including analyte through a detector sample flowchannel, (b) detecting the concentration of analyte in the sample flowchannel and generating an electrical signal in response to the detectedconcentration of the analyte, (c) providing an electrolytic electrolytegenerator having first and second electrodes in electrical communicationwith the electrical signal, (d) passing the generated electrical signalto the first and second electrodes to generate electrolyte aqueoussolution, and (e) detecting electrolyte solution generated in the eluentgenerator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-9 are schematic diagrams of devices and systems according to theinvention.

FIGS. 10-17 illustrate experimental results according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is applicable to detection of current or potentialgenerated ionics by ionic species in a sample solution in a variety ofanalytical techniques.

FIG. 1 illustrates an ion detector 62 using an electrolytic ion transferdevice. An aqueous stream 10 is directed to a sample injection 12 inwhich an electrolyte sample is injected. From there, the aqueous samplestream flows in conduit 14 to electrolytic ion transfer device 16, whichincludes a liquid sample flow-through channel 18, e.g. in tubular form,having an inlet 18 a and an outlet 18 b. Charged barriers in the form ofion exchange beads 20 and 22 are disposed on opposite sides offlow-through channel 18. As illustrated, bead 20 is a cation exchangebead and bead 22 is an anion exchange bead. Such beads are capable ofpassing ions of one charge, positive or negative, and of blocking bulkliquid flow. Beads 20 and 22 may include exchangeable ions of the samecharge or of opposite charge. Tubes 24 and 26, formed of anon-conductive material, e.g. a plastic such as PEEK, define liquidreservoirs 24 a and 26 b, respectively. As illustrated, beads 20 and 22are in fluid communication with reservoirs 24 a and 26 b and with sampleflow channel 18. The structure of device 16 and the seating of the beadsin recesses of tubes 24 and 26 to form a seal is described in U.S.patent application Ser. No. 11/940,892 (“the '892 application”) filedNov. 15, 2007, incorporated herein by reference. For example, the sealmay be formed by inserting the beads in a dry form and then wetting themto expand them into tight seals in the recesses.

As illustrated, an aqueous stream, with or without an electrolyte, flowsthrough the interior of tubes 28 a and 28 b, disposed in chambers 24 aand 26 b to direct aqueous solution to outlets in the chambers (notshown) close to the beads. The tubes serve as oppositely chargedelectrodes and so are formed of electrically conductive metal, e.g.platinum. It should be noted that the electrodes could be conductivemetal wires in place of the tubing configuration. The aqueous streamflows out the chambers through ports not shown. Tubes 28 a and 28 bserve as electrodes of opposite polarity and are connected to a directcurrent power source at 30. Also as illustrated, an electrical signal(e.g. current or voltage) detector 32, illustrated in the form of acurrent meter 32 is in an electrical circuit with lead 28 c from tubularelectrode 28 c and lead 28 d from tubular electrode 28 b. In contrast toFIG. 1 of the '892 application, the present invention includeselectrical signal detector 32 in electrical communication in series withelectrodes 28 a and 28 b. A current meter is useful for a constantvoltage system. Alternatively, for a constant current system, a voltagemeter may be employed. Signal detector 32 detects the electrical signalchange caused by transport of ions in the aqueous sample stream flowingthrough channel 18 across beads 20 and 22 into the aqueous liquid inchambers 24 a and 26 a.

Detector 62 is illustrated using two beads separating two chambers fromthe sample flow-through channel. However, if desired, a single barrier,in the form of a bead, may be employed together with only a singlechamber on the opposite side of the bead. In this instance, oneelectrode is in electrical communication with the sample flow channelwhile the other is in electrical communication with the chamber on theopposite side of the bead.

For a system in which the beads are of opposite charge, detector 62 isreferred to as forward-biased, when the electrode (28 a) behind thecation exchange bead (22) is positive with respect to the electrode (28b) behind the anion exchange bead (20) and reverse biased with theopposite electrode polarity of the electrodes. Under the forward biasconditions, the device with appropriate electrolytes in each chamberwould generate an electrolyte, e.g. an acid, base or salt. For example,with 1 M sodium hydroxide flowing behind the cation exchange bead 20,the device would generate sodium hydroxide in the sample flow channelwhen operated in the forward bias mode. When powered, device 16generates hydronium ions at anode 28 a and sodium ions in chambers 24 awould be transported across cation exchange bead 20. Similarly,hydroxide ions would be generated at the cathode 28 b and would betransported across anion exchange bead 22 into the sample solution insample flow channel 18 to form sodium hydroxide. The concentration ofthe sodium hydroxide could be calculated from the current applied on thedevice.

Under the reverse biased mode, device 16 would behave as a chargedetector. For example, after injecting sodium chloride sample intoaqueous stream 14 and flowing it through sample flow channel 18, thesodium ions would be driven across the cation exchange bead 20 towardscathode 28 b, and the chloride ions would be driven across the anionexchange bead towards anode 28 a. Water is formed in sample flow channel18. With a sufficient residence time and magnitude of the appliedelectric field, the electrolyte is completely removed from the sample,and the resulting integrated current pulse generated is directlyreflective of the total charge injected. Thus, the device behaves as acharge detector regardless of (a) the electrical mobility of the ionsinvolved and (b), unlike coloumetry, whether they can be oxidized orreduced in an aqueous stream.

The transport of the charged ions to the electrode chambers is governedby both the hydrodynamic mass transport and the charge transport underthe electric field. If the residence time in the device is long enough(the flow rate is slow enough) and the electric field is high enough,the peak area in coulombs is strictly Faradaically related to the totalamount of charge injected into the system. At a given flow rate, thepeak area increases with increasing electric field (applied voltage) andreaches a plateau value until all the charge is transferred. It shouldbe understood that the necessary electric field to reach this plateau isdependent on the residence time, the plateau is attained at lowerapplied voltages as the residence time increases. The preferred voltagerange is 1.5-100 volts more preferably 2-20 volts and most preferably3-15 volts.

In another embodiment, instead of ion exchange beads forming the chargedbarriers which pass ions of one charge, positive or negative, but whichblocks liquid flow, as illustrated in FIG. 1, ion exchange membranes maybe used. An electrolytic device of this type may be as illustrated inthe suppressor of U.S. Pat. No. 5,352,360 or the acid or base generationapparatus of U.S. Pat. No. 6,225,129 or 5,045,204, incorporated hereinby reference. Such a device may include a single ion exchange membraneseparating the sample flow channel from a liquid reservoir on theopposite side of it, or two ion exchange membranes corresponding to thetwo bead approach of FIG. 1. However, the systems disclosed in suchdevices do not include an electric signal detector.

As illustrated in FIG. 1, electrodes 28 a and 28 b are in the form oftubes which serve as conduits for flowing liquid solution into thechambers at 24 a and 26 a. Alternatively, the electrodes may beconventional electrodes, and the solution may be transported to thechambers through some other inlet. As illustrated, the solution inchambers is supplied as a flowing solution. In some instances, suchsolution may be a large reservoir of substantially nonflowing solution.In this case, appropriate vents for venting the electrolytic gases isprovided.

The invention will be now described with respect to a system ofsuppressed ion chromatography. Referring to FIG. 2, an embodiment of theinvention is illustrated in which an electrolytic ion transfer device isdisposed downstream from a chromatography column and electrolyticsuppressor in a suppressed ion chromatography system. Pump 48 pumpseluent or an aqueous liquid stream without an electrolyte (collectivelycalled “an aqueous stream” unless otherwise specified) through a sampleinjection valve 50. The aqueous stream including sample, also referredto as “the sample stream,” flows through conduit 52 into the inlet ofchromatography column 54. This portion of the system may be anyconventional chromatography system with conventional optional auxiliaryguard columns, concentrator columns, and the like. The chromatographycolumn typically includes a packed bed of ion exchange resin or otherion exchange medium such as an ion exchange monolith with flow-throughpassages such as illustrated in U.S. Pat. No. 7,074,331. The aqueousstream eluting from the outlet of column 54 is directed by conduit 56into the sample flow channel 58 a of electrolytic suppressor 58, e.g.,of the type illustrated in U.S. Pat. No. 5,352,360. Sample flow channel58 a is separated from a regenerant flow channel 58 b by an ion exchangebarrier 58 c in the form of an ion exchange membrane. Other knownsuppressors may also be used for the suppressor in the suppressed ionchromatography system with appropriate plumbing changes.

As illustrated in FIG. 2, detector 62 may be of a type illustrated inU.S. Pat. No. 6,225,129 4,999,098, 6,328,885 or 5,045,204, includingonly a single ion exchange membrane 62 a separating ion receiving flowchannel 62 c. A constant current power supply 76 supplies constantcurrent to electrodes, not shown, in electrical communication withchannel 62 b and chamber 62 c respectively, through lead 74. Thedetector 62 operates as illustrated in FIG. 1 except for thesubstitution of the ion exchange membrane for the bead. Thus, theelectrical circuit includes an electrical signal detector 32, such as acurrent meter in electrical communication with the two electrodes andpower source.

Referring again to FIG. 2, the effluent solution exiting the sample flowchannel 60 of detector 62 may be routed by a conduit 64 to an optionaldetector cell 66, preferably a detector conductivity cell 66 of the typeknown in the art. In this embodiment, a constant current power supply 76is connected to detector 62 by lead 74 and the response to the appliedcurrent is monitored as a voltage. Any change in voltage is correlatedto the analyte and detected as a peak.

In one embodiment, detector 62 is a 100% current efficient device, inthat it draws only the current that is transported across the sampleflow channel by the electrolyte in that channel. 100% current efficiencydevices are described in U.S. Pat. No. 6,328,886, U.S. Pat. Nos.6,077,434 and 6,808,608. In one embodiment the sample flow channel is aneutral screen thereby enabling the current to be carried by theelectrolyte in that channel. For example a suppressor device of theprior art sold commercially as an ASRS 300 suppressor from DionexCorporation when built with an eluent channel that is fitted with aneutral screen the device as disclosed in U.S. Pat. No. 6,328,886becomes 100% current efficient in that the device only draws the currentrequired to suppress a given eluent strength. The device is preferablyoperated in the constant voltage mode. Such a device would be suitableas the detector 62 of the present invention. The current efficiency ofthe device of 62 is preferably 40-100%, more preferably 60-100% and mostpreferably 80-100%.

If power supply 72 is operated in a constant voltage mode, a variablecurrent is produced that can be correlated to the specific ionic speciesof the sample stream flowing a sample flow channel 62 b.

As illustrated, the cell effluent from optional detector cell 66 isrouted back as a recycle stream to suppressor 58 via conduit 68 tosupply water for the regenerant flow channel 58 b of suppressor 58. Thesuppressor waste from channel 58 b is routed via conduit 70 to supplywater required for the electrolysis reactions in chamber 62 c ofdetector 62. Waste can be diverted to waste via line 78 or routed toother devices for supplying water required for electrolysis reactions oras a sink for removing gases across a gas permeable bulk liquid barrierin devices of the prior art. The routing of the cell effluent could alsobe routed first to chamber 62 c in the detector module 62, followed byrouting it to the regenerant channel 58 b of the suppressor 58.

Referring again to FIG. 2, in operation, an aqueous stream containingeluent (electrolyte) is pumped from a source container (not shown) by apump 48 and routed through injection valve 50 in which liquid samplesolution is injected for analysis in an ion chromatography (IC) system.The aqueous sample stream eluting from valve 50 is routed tochromatography column 54 in which the sample ionic species are separatedand routed to suppressor 58 for suppressing the eluent and convertingthe sample counterions to acid or base form. The suppressor eluent flowsto the electrolytic detector device 62 operated in conjunction with thepower supply 76. Here, detector 62 is operated in the constant voltagemode at approximately 100% current efficiency because any current drawnby the device could be easily correlated to the ionic content flowingthrough the sample flow channel. When an analyte peak is transportedacross sample flow channel or charge barrier 62 a, there is a change inthe current (detected by detector 32 of FIG. 1 but not shown in FIG. 2).For a 100% current efficiency device, the current is directlycorrelatable to the concentration of the analyte of interest. Asillustrated, the aqueous stream can also be routed to an optionaldetector cell 66.

As described for FIG. 2, a change in current is monitored. In anotherembodiment, a change in voltage is detected. In another embodiment, thedevice can be operated at constant current. In one embodiment the devicecan be operated with no applied current and in this case the voltageacross the device is monitored. A change in the voltage induced by anelectrolyte injection in the sample flow channel results in thedetection of the electrolyte.

For anion analysis, the suppressor device of 58 has ion exchangemembrane barrier 58 c is cationic. Detector 62 could have a barrier 62 aof the same cation exchange functionality. Under this condition, thedetector 62 will not retain the analyte ions since it is similar to thesuppressor in configuration. The transition of an electrolyte or analytepeak through the sample flow channel results in a change in electricalproperty of the detector 62 as measured by a change in current whenoperating in the constant voltage mode or a change in voltage in theconstant current mode.

In another embodiment, for anion analysis, detector barrier 62 a, e.g.of cation exchange functionality, could have an opposite functionalcharge (anionic exchange functionality) to that of suppressor barrier 58c (of cation exchange functionality). In this embodiment, the analyteanions in flow channel 62 b will be retained by barrier 62 a and will bedriven out across that barrier into chamber 62 c. In this embodiment,the change in current induced by an electrolyte present in the sampleflow channel (when operated at a constant voltage, or voltage changewhen operated at a constant current) will be used as the detectorsignal. Since the analyte is removed in this embodiment, optionaldetector 66 if used preferably is placed in conduit 60 downstream fromsuppressor 58 and upstream from detector device 62.

In another embodiment illustrated in FIG. 3, the detector of the presentinvention serves as a combination detector and suppressor. Like partswith FIG. 2 will be designated with like numbers. The principaldifference between the embodiments of FIGS. 2 and 3 is that there is noseparate suppressor 58 in FIG. 3. As in the device of FIG. 1, a changein the electrical signal, such as voltage, detected by signal detector32, when the device is operated under constant current conditions,enables detection of the sample analyte. Optional detector 66 can bedownstream of detector 62 since the analyte peak is unretained by thedetector. In this embodiment, except for detection by signal detector32, detector device 62 operates like a suppressor of the prior art, e.g.as set forth in U.S. Pat. No. 5,352,360 or as sold as ASRS 300. Thedevice would be operated in constant current mode and the voltage ismonitored using signal detector 32 (not shown). In comparison to FIG. 2since there is no additional detector the band dispersion is minimizedleading to higher efficiencies for early eluting peaks. This will be asignificant advantage for some applications since peak resolution wouldbe improved due to lower dispersion volumes.

A 100% current efficient water purifier as disclosed in U.S. Pat. No.6,808,608 could also be used in this embodiment. In this instance theeluent and the analyte ion will be removed as per the present invention.If the above device is operated in the constant current mode a change involtage with the transition of the analyte peaks could be used as asignal for detecting the ions of interest. The change in voltage couldbe correlated to the concentration of the species of interest. In analternate embodiment the 100% current efficient water purifier could beused to monitor the water quality in a flowing water stream. The devicecurrent is indicative of the ionic content of the water stream whenoperated with constant voltage.

FIG. 4 is similar to FIG. 3 except that the separator (chromatographiccolumn) is an electro-elution chromatographic column such as illustratedin U.S. Pat. No. 6,793,327, particularly at columns 11-18, incorporatedherein by reference. Here, chromatography column 54 includes ionexchange medium, e.g. a packed bed of ion exchange medium 54 a, andflow-through electrodes 80 and 82 near the inlet and outlet of the bedconnected to a power source, not shown, which passes current between theelectrodes through the media. An aqueous stream pumped by pump 48 may bean electrolyte-containing eluent or a water stream, as discussed in the'327 patent. Electrolysis gases would be generated in line. Thus, it ispreferable to include a gas removal device such as a catalyst column asdescribed in U.S. Pat. No. 7,329,346, or a gas permeable membranedevice, in conduit 56, as is known in the art. Removal of theelectrolyte gases lowers the noise characteristics of the electricalsignal in detector 62. Plumbing details are similar to those withrespect to FIG. 1. When detector device 62 is operated in constantcurrent mode a change in voltage in response to the analyte peak wouldbe correlatable to the concentration of the analyte.

FIG. 5 illustrates another form of detector according to the invention.Two ion exchange membranes, 112 and 114 define three fluid flow-throughchannels 116, 118 and 120 in a suppressor fitted respectively withgasketed screens 116 a, 118 a and 120 a in the channels. Two electrodes110 flank screens 116 a and 120 a, respectively. In operation, anaqueous stream 122 containing sample analyte is routed through channel118, and the effluent from channel 118 is routed out of the device atoutlet 124. Channels 116 and 120 are fed with recycling aqueous stream124, designated 126 and 128, respectively, or an external aqueous streamand are routed to exit the device in lines 130 and 132. When the analytepeaks are unretained, e.g., for anion analysis when the membranes 112and 114 are cation exchange membranes, the detector is preferably usedafter a suppressor in a suppressed IC system for anion analysis similarto that described in U.S. Pat. No. 5,352,360. For anion analysis, themembranes in this embodiment are both cation exchange membranes and donot retain the analyte anions. Screens 116 and 120 are preferably ionexchange membranes of the same while screen 118 is neutral resulting inapproximately 100% efficient embodiment. By monitoring the current whenthe device is operated with constant applied voltage, current detectionof various species can be accomplished using a current meter such asdetector 32 in the circuitry of FIG. 1. When the device is used forcation analysis, the analyte cations are retained and removed in theregenerant channels 116 and 120.

The device of FIG. 5 can be constructed like a water purifier device.Here, the membranes 112 and 114 are oppositely charged (anion exchangeand cation exchange membranes, or vice versa). This is a salt-splittingconfiguration and would allow removal of analyte ions and counterions.Screen 116 a is preferably an anion exchange screen and screen 120 a ispreferably a cation exchange screen. The central channel is neutral andcan include a neutral screen 118 a and allows the device to be 100%current efficient. When this device is used after a suppressor in thesuppressed IC system, the device removes anions via the anion exchangemembrane when the electrode on the opposite side of the sample flowchannel is an anode and removes cations via a cation exchange screenwhen the electrode on the opposite side of the sample flow channel is acathode. Such removal of ions results in a current proportional to thesample ionic species concentration for detection by a signal detector inthe circuitry of FIG. 1.

A water purifier such as illustrated in FIG. 5 or other conventionalelectrolytic membrane-based water purifier can be used as the detectordevice 62 of FIG. 1 independent of a chromatography system. In onepreferred embodiment, the current from a 100% water purifier unit thatis operated in the constant voltage mode is directly correlated to theionic content of the water stream. This provides a useful tool to gaugethe water purity. If needed other process steps could be triggered basedon the signal feedback from the device of the present invention. Here,the device of FIG. 5 is used as an ion transfer device 62 in thecircuitry of FIG. 1 in which the current detected by current meter 62 iscorrelated to the ion content of the water stream to be purified.

The above ion detector device and systems of the present invention havebeen described with respect to an ion detector which includes a samplechannel separated by an ion exchange barrier from an ion receivingchamber including a reservoir in which an aqueous solution is retained,preferably supplied in a flowing stream. Sample ionic species aretransported across the ion exchange barrier. In another embodiment,illustrated in FIG. 6, the ion detector is in the form of anelectrolytic device including a housing or column, without an ionexchange barrier, packed with ion exchange medium, such as ion exchangeresin or an ion exchange monolith, and including electrolytes forapplying a current across the medium. The sample solution flows throughthe medium. This system is used in place of the ion transfer devicesincluding the ion exchange barrier embodiments described above. Thisdevice may be constructed as illustrated in U.S. Pat. No. 6,093,327except for the presence of the signal detector in the electrical circuitwith the electrodes and power supply as illustrated. Column 38 is packedwith ion exchange resin in a bed 38 a, fitted with a flow-through inletelectrode 34 and flow-through outlet electrode 36, in substantiallyintimate contact with the ion exchange resin bed 38 a. In operation anaqueous sample stream 40 flows through electrode 34 into resin bed 38 aand flows out as effluent stream 42 through electrode 36. A powersupply, not shown, e.g., the constant current power supply 76 in FIG. 3,is connected to electrodes 34 and 36. Similarly, a signal detector 32,e.g., in the form of a current meter is in an electrical circuitincluding the power supply and two electrodes, as illustrated in FIG. 1.This device may be used in place of ion transfer detector 62 withappropriate differences in plumbing. Thus, it can be disposed after thesuppressor in the suppressed IC system of FIG. 2, or may be used as acombined suppressor/detector as illustrated in FIG. 3.

In one configuration of FIG. 6, the ion device does not retain theanalyte ions and the transition in electrical property as a result ofthe analyte peak is recorded and used as the detection signal, e.g., incurrent meter 32 of FIG. 1. The device would be operated under constantcurrent, and the device voltage (a measure of the device resistance), ismonitored as a detector signal by detector 32 of FIG. 1. Here, thedevice is regenerated since its capacity is depleted by the eluentcounterions. For example, when analyzing anions, the packing may be acation exchange resin bed. The device would not retain the anion analyteions, such as chloride, but would retain the eluent counterions such assodium. Here, the device can be used as a suppressor, which can beregenerated as is known in the prior art. In another embodiment, deviceretains the analyte ions but not the eluent ions, and a change inelectrical resistance is monitored by the signal. For example, whenanalyzing anions the device can be packed with an anion exchange resinwhich would retain the analyte ions.

It should be noted that the above device of FIG. 6 could also beoperated as an electrolytic electrolyte generator of the presentinvention. In this configuration the ion exchange media has exchangeableions that are in the desired electrolyte form.

FIG. 7 is an embodiment of the ion exchange barrier-free approach ofFIG. 5 utilizing an electro-elution chromatography column, as in FIG. 4,but in which the chromatography column serves the dual purposes ofseparation and detection. Like parts with FIG. 4 will be designated withlike numbers. Electrodes 80 and 82 are powered by power supply 76 usingpower supply leads 74. As in the electrical setup of FIG. 1, anelectrical signal detector 32, not shown, is in the electrical circuitconnecting electrodes 80 and 82 and power source 76.

Before sample injection in injector 50, the ion exchange medium incolumn 54 has a relatively low resistance. After sample injection,column resistance increases due to the retention of sample ions on thecolumn. As electro-elution proceeds and as the analyte peaks elute offthe column, the device resistance decreases. A plot of resistance versustime as detected by a current meter, not shown, in the circuitry of theelectrodes as illustrated in FIG. 1, allows determination of theconcentration of the analyte ions.

The embodiment of FIG. 8 is similar to the system of FIG. 3 in that itincludes a combination suppressor/detector. However, it uses theapproach of FIG. 5 for a charged barrier-free suppressor device withthree outlets. The general flow system and construction of thesuppressor device may be as illustrated in U.S. Pat. No. 6,468,804,incorporated herein by reference. Specifically, the ion detector issimilar to that of FIG. 5 of the '804 patent, except that the influentstream is split into multiple outlet streams, 42, 44 and 46. Streams 44and 46 flow past electrodes 34 and 36 as separate streams. In FIG. 5 ofthe '804 patent, detection of the analyte peaks is measured either bydiverting stream 42 to a detector cell or by measurement by a separatepair of electrodes in the device. In contrast, in the device of FIG. 8herein, the need for a separate detector cell or separate electrodes iseliminated. The signal detector is in the electrical circuit with thepower supply and two electrodes, as illustrated in FIG. 1. Thisembodiment can be used as a detector device 62 downstream from thesuppressor in a suppressed IC system. Alternatively, it may be used as adifferent form of combination suppressor and detector, as illustrated inFIG. 3.

In the embodiment of FIG. 9, an electrical signal detector is not inelectrical communication with the electrodes 28 a and 28 b of the deviceof FIG. 1. Instead, the ion transfer device is used in combination witha downstream electrolytic electrolyte generator in which the currentgenerated in the electrical circuit of the ion transfer device is usedto generate electrolyte which is detected by known methods. In oneembodiment of the electrolyte generator, a second pair of electrodes isin electrical communication with the ion transfer device electrodes, andwith an electrode source reservoir and an electrolyte generationchamber, respectively. A conventional detector, such as a conductivitycell, for the electrolyte generated in the electrolyte generationchamber may be placed in fluid communication with that chamber.

Specifically, in the embodiment of FIG. 9, the device includes anelectrolytic ion transfer device, e.g., as illustrated in FIG. 1, orwhich, as illustrated in FIG. 2, uses an ion exchange membrane insteadof the beads in FIG. 1, coupled to an electrolytic electrolytegenerator. Thus, the electrolytic ion transfer device portion includesall of the elements illustrated in FIG. 1 except for the current meter32. As illustrated, this single charged barrier ion transfer deviceincludes (a) a sample flow-through channel, (b) a charged barrierdisposed along the sample flow-through channel in fluid communicationtherewith, (c) a chamber disposed on the opposite side of the chargedbarrier from the sample flow-through channel, and (d) first and secondelectrodes in electrical communication with the chamber and sampleflow-through channel, respectively.

In addition, the system includes an electrolytic electrolyte generatorhaving (a) an electrolyte source reservoir, (b) an electrolytegeneration chamber, (c) a charged barrier, e.g., of the same type as theion transfer device barrier disposed between the electrolyte sourcereservoir and the electrolyte generation chamber, and (d) a pair ofelectrodes in electrical communication with the ion transfer deviceelectrodes, and with an electrolyte source reservoir, and with theelectrolyte generation chamber, respectively. A conventional detector,such as a conductivity detector, may be provided for monitoring thegenerated electrolyte. The electrolytic electrolyte component may be oneof the configurations illustrated in the acid or base generationapparatus of U.S. Pat. No. 6,225,129 or 5,045,204 except that thecurrent is supplied to the electrodes in electrical communication withthe electrodes of ion transfer device 62 powered by power supply 30.

A second charged barrier may be disposed along the sample flow-throughchannel in fluid communication with a second chamber being disposed onthe opposite side of the second charged barrier from the sampleflow-through channel. Where two charged barriers are used, they may beof the same or of opposite charge, and may be any of the forms describedfor the electrolyte ion transfer device, such as ion exchange beads orion exchange membranes.

An advantage of including the second charge barrier is that theelectrolytic gases are no longer in the product stream. Such devices areillustrated in U.S. Pat. No. 5,045,204. The second charge barrier canhave the same charge and as illustrated in FIG. 5 of U.S. Pat. No.5,045,204. The base generated in the cathode chamber overcomes theDonnan potential. Electrolyte is produced in response to application ofa current. An advantage of this embodiment is that the generated basedoes not contain any anions. When the second charged barrier has anopposite charge, then the hydroxide or other anions in the sample flowchannel are transported across the anion exchange barrier, while sodiumor other cations in the sample flow channel are transported across thecation exchange barrier to combine and form electrolyte in the sampleflow channel. In this approach however other anions present in theelectrode chamber close to the anion exchange barrier may also betransported across the barrier.

An advantage of generating a different electrolyte in response to asignal in the first ion transfer device detector is that now the analytecould be transformed to a species that is more suited for a givendetection mode. For example if the generated species is methanesulfonicacid (MSA), it can be detected by other means such as a conductivitydetection or SIM mode by mass spectrometry. Weak acids such as borate orsilicate are difficult to be detected by suppressed conductivitydetection. By using the present invention, the transformation of thespecies to, say, MSA, would significantly improve the detection with theconductivity detector.

Referring specifically to FIG. 9, both the ion transfer device and theelectrolyte generator have the general structure and operation of iontransfer device 62 of FIG. 1 with the exception of (1) oppositepolarities of the electrodes in the electrolyte generator, (2) theabsence of a signal detector 32, and (c) the electrical circuitconnecting the two devices. Like parts will be designated with likenumbers.

As illustrated, the ion transfer device 62 of FIG. 9 is in a reversebias mode and is connected to electrolyte generator 63 in a forward biasmode. Thus, as illustrated, in device 62 electrode 28 a is a cathode,electrode 28 b is an anode, bead 20 is a cation exchange bead and bead22 is an anion exchange bead. In generator 63, electrode 28 e is ananode connected to cathodic electrode 28 a by lead 28 c and electrode 28f is a cathode connected to the cathodic terminal of a power supplydevice 30. The anodic terminal of the power supply is connected to theanode electrode 28 b by lead 28 d. Power supply 30 is illustrated in thecircuitry along lead 28 d. A salt electrolyte, KNO₃, is illustrated asbeing supplied to the chambers into which electrodes 28 e and 28 fproject in electrolyte generator 63.

In another embodiment, the electrical signal supplied to electrodes 28 eand 28 f of generator 63 in FIG. 9 is the electrical signal produced bya conventional detector. Conventional chromatography detectors usuallygenerate a current or voltage signal in response to an analyte. Forexample, with conductivity detection a current is generated in responseto the presence of analyte (transition of a peak). This current istypically amplified and converted to a digital format. In addition thecurrent is available as an output signal in the detector in the form ofan analog output. The output signal is typically used for printing orfor data analysis by converting it back to digital using A/D converters.According to the present invention, the electrical signal from thedetection process or subsequent signal after amplification or conversionto digital format is electrically coupled to an electrolytic such asgenerator 63 in FIG. 9, or other generator of the prior art, or iontransfer device 62 in FIG. 9 in the forward bias mode, to generateelectrolyte in response to a signal in the conductivity detector. Thetransferred signal may be processed or amplified if needed prior toconnecting to the leads 28 e and 28 f on the generator 63.

Any detector which produce an electrical signal in response to ananalyte could be used. Common detectors include conductivity detectorsor photomultipliers. The latter are extremely sensitive light detectorsthat provide a current output proportional to light intensity. They areused to measure any process that directly or indirectly emit light.Other suitable detectors include amperometric detector and diode arraydetector. It should be noted that any detector of the prior art could besuitable with the above embodiment of the present invention.

The signal for example can be an analog signal, sampled signal from ananalog to digital convertor (A/D), a mathematically calculated signalfrom an analog or digital signal or an amplified signal. The detectorsignal could be used to drive the electrolyte generator thus generatinga pulse of reagent in response to a peak traversing the also detector ofthe prior art. Thus the detector signal is transformed to a chemicalsignal in the form of the generated reagent electrolyte acid, base orsalt solution. It is advantageous to be able to generate a differentspecies to facilitate detection using a more suitable detector forcertain applications. Additionally it is possible to amplify the signalchemically by producing the reagent at a much higher concentration bypumping a DI water stream into the sample flow channel of theelectrolytic generator at a low flow rate relative to the flow rate ofthe original detector setup through which the analyte of interest wasdetected.

A specific apparatus of this type for detecting analyte in a samplesolution includes (a) a detector sample flow channel for liquid samplecontaining analyte, (b) a signal detector operatively associated withthe detector sample flow channel for detecting analyte in liquid sampletherein, the signal detector generating an electrical signal in responseto the concentration of the analyte, (c) an electrolytic electrolytegenerator comprising (1) a first electrolyte source reservoir, (2) afirst electrolyte generation chamber, (3) a first electrolyte chargedbarrier capable of passing ions of one charge, positive or negative, andof blocking bulk liquid flow, disposed between the first electrolytesource reservoir and the first electrolyte generation chamber, and (4)first and second electrodes in an electrical circuit with electricalcommunication with the detector generated electric signal, and with thefirst electrode source reservoir and the electrolyte generation chamber,respectively, and (d) an electrolyte detector for the electrolytegenerated in the electrolyte generation chamber in fluid communicationtherewith.

A method for detecting analytes in a sample solution using this approachincludes the steps of (a) flowing an aqueous sample stream includinganalyte through a detector sample flow channel, (b) detecting theconcentration of analyte in the sample flow channel and generating anelectrical signal in response to the detected concentration of theanalyte, (c) providing an electrolytic electrolyte generator comprisinga first electrolyte source reservoir separated from an electrolytegenerating chamber by a second charged barrier having exchangeable ionscapable of passing ions of one charge, positive or negative, (d) flowingan aqueous solution through the electrolyte generating chamber, (e)passing the generated electrical signal across to first and secondelectrodes of opposite polarity, in electrical communication withsolution in the first electrolyte source reservoir and in the firstelectrolyte generating chamber, respectively, to pass ions of onecharge, positive or negative, through the second charged barrier togenerate electrolyte aqueous solution in the first electrolytegeneration chamber, and (f) detecting the generated electrolytesolution.

Any form of electrolytic electrolyte generator may be substituted forelectrolyte generator 63 in the combination ion transferdevice/electrolytic electrolyte generator of FIG. 9 or in thecombination conventional detector (e.g. conductivitydetector)/electrolytic generator described herein. Thus, for example, anelectrolytic electrolyte (eluent) generator packed with flow-through ionexchange medium, e.g. a packed bed of ion exchange resin, as disclosedin U.S. Pat. No. 6,316,271, incorporated herein by reference, e.g. atFIG. 2, may be used with the connecting electrical circuitry between theion transfer device or conventional detector and the electrolyticelectrolyte generator electrodes as described herein. Such anelectrolytic ion exchange medium device is also illustrated at FIG. 6herein. The electrolyte generated in the generator flows to aconventional detector, e.g. a conductivity detector for detection.

The following non-limiting examples illustrate the present invention.

Example 1

Using the device of FIG. 1, the arrangement as forward biased when theelectrode behind the CER bead is positive with respect to the electrodebehind AER bead and reverse biased with the opposite electrode polarity.

FIG. 10 shows the diode behavior of such devices. Trace (a) shows thei-V plot when 20 mM KOH and 1 mM H₂SO₄ are respectively present behindthe AER/CER beads; (b) shows the case when the CER/AER electrolytes areboth 10 mM KNO₃. In both cases, water flows through the central channel.(As illustrated, Trace (a) is the longer plotted line on the right sideof the Y-axis.

Note that in both cases (a) and (b), the device behaves as a diode. In(b), under forward-biased conditions, H⁺ and K⁺ are respectivelytransported through the CER bead while OH⁻ and NO₃ ⁻ are respectivelytransported through the AER bead to form water and product KNO₃ in thecentral channel. The H⁺ or Predictably, if the AER and CER beads,representing the charge-selective gates, are removed, diode behaviordisappears altogether. Also notable is that in case (b), the amount ofKNO₃ produced in the central channel closely adheres to what is expectedon the basis of Faradaic equivalence [9]. The above illustrates thegenerator like behavior of the diode like device of the presentinvention when operated in the forward bias mode.

Example 2

FIG. 11 shows the behavior of the reverse-biased ionic diode. The samevolume (1 μL) of different electrolyte samples are injected into thecentral sample flow channel in a DI water stream flowing at 4 μL/min.The applied voltage was 14 V and the CER/AER electrolytes were 20 mMKNO₃. It will be noted that equivalent amounts of NaNO₃, KCl, HNO₃,BaCl₂, or K₃PO₄ all have the same signal (the peak area of theindividual responses shown are 194±16 microcoulombs), very differentfrom that of a conductivity detector [10]. The advantage of the sameresponse for equimolar quantities of various salts is that a universalcalibration becomes feasible and only one analyte needs to be used forthe calibration aspect. This greatly reduces the standard preparationand run time during calibration.

Example 3

FIG. 12 shows optimization studies of response versus flow rate. A 1 μLsample of 0.8 mM KCl was injected. The effluent conductivity for 3μL/min flow rate is shown. As the detector signal reaches a plateau, theeffluent is deionized. For clarity, the standard deviation is shown onlyfor the 3 μL/min data, others are comparable. At a given flow rate, thepeak area increases with increasing electric field (applied voltage) andreaches a plateau value until all the charge is transferred. It will beunderstood that the necessary electric field to reach this plateau isdependent on the residence time and as shown in FIG. 12, the plateau isattained at lower applied voltages as the residence time increases. Notshown here is the corollary case that at a fixed applied voltage, peakarea reaches a constant plateau value as flow rate is decreased.

Example 4

The dependence of the observed peak area upon flow rate for a weak and astrong electrolyte is shown in FIG. 13. Applied voltage was 14 V, and asample of 1 mM KCl and 1 mM boric acid are injected respectively. Itwill also be observed that the charge detector is effectively anelectrically operated deionizer. An interesting consequence of this isthe ready ability to remove, e.g., salt from a mixture of sugar andsalt, not shown here. Perhaps more interesting is the potential abilityof a charge detector to discriminate between a strong electrolyte and aweak electrolyte. Consider a case where the central channel flow rate ismodestly high, mass transport to the beads is not quantitative. The sameconcentrations of a strong and weak electrolyte solution are beingseparately injected. Naturally, the strong electrolyte produces a muchgreater signal. As the flow rate is reduced, the signal from the weakelectrolyte increases relatively much more because as these ions areremoved, further ionization of the unionized material must occur whereasthe ions in the strong electrolyte case were already mostly removed.Increasing the residence time for a weak electrolyte therefore resultsin a continued increase in signal; in the extreme case, under stoppedflow conditions, charge transfer will take place until all theelectrolyte is removed.

Example 5

This example uses the apparatus of FIG. 9 including an ion transferdevice 62 that is electrically connected in series to a forward biascharge detector electrolytic generator 63. A DI water stream is pumpedat 10 μL/min in sample flow channel 18 of the device 62 that is operatedin the reversed bias mode. The polarity is such that anode 28 b isadjacent to the anion exchange bead 22 a thus aiding removal of anionsand cathode 28 a is adjacent to cation exchange bead thus aiding removalof cations. A forward bias electrolytic generator 63 is electricallyconnected to device 62. A DI water stream is pumped in line 14 a at 1.6μL/min into flow channel 18 a of generator 63 and is routed to a UV cellin a detector (not shown) and monitored at 210 nm. The chambers forelectrodes 28 e and 28 f are supplied with 20 mM KNO3 source ions. Theelectrodes of device 62 and generator 63 are connected electrically inseries such that for a given potential, a current generated in device 62is transmitted at substantially the same level to the generator 63. Whenan injection plug of 1 μL of 1 mM NaCl is injected into injector 12 acurrent is produced in device 62 that is transmitted to the electrodesof generator 63 that generates a equivalent amount of potassium nitrate.A peak is observed in the UV trace. FIG. 14 shows how a pulse of NaClinjected into the charge detector can be optically detected by atranslated equivalent amount of KNO₃ generated using an electrolyticgenerator of the present invention that is coupled electrically inseries. While the reversed biased diode behaves as a charge detector,with appropriate electrolytes on each side, the forward biased diode isa Faradaic chemical generator as shown in Example 1. In much the sameway that in a light emitting diode (LED) hole-electron recombinationproduces different colored light, passage of A⁺ through the CER and B⁻through the AER to form different AB compounds in the central channel iscompletely dependent on the choice of the CER and AER electrolytes AXand YB, respectively. Much as a solar cell can be used to light an LEDof any chosen color when connected in series, if a reverse-biased chargedetector is connected in series with a forward-biased chemical generatoralong with a voltage source of adequate magnitude, the voltage dropoccurs almost entirely across the reverse-biased charge detector. If anyelectrolyte is injected into the charge detector, the resulting currentpasses through the generator producing an equivalent impulse of anotherelectrolyte that is user chosen. Concentration amplification can bereadily performed by such serial systems because the charge detector canbe a large area macroscale device that can be used to detect amacroscale injection while the same current is made to flow through amuch smaller generator device where the same equivalents of the desiredchemical is generated in a much smaller flow rate, potentiallypermitting enhanced detectability with a concentration sensitivedetector

Example 6

A 100% current efficient water purifier was built following the Example1 in U.S. Pat. No. 6,808,608. The cation exchange membrane was a 0.005″thick membrane and the anion exchange membrane was 0.003″ thickmembrane. Finally, in semiconductor diodes, Zener diodes are made bydecreasing the thickness of the junction, so avalanche breakdown occurs.In the present case, if the ion exchange material thickness is graduallyreduced, it becomes possible to observe similar breakdown, as shown inFIG. 15 for a device in which the ion exchange resin beads in theprevious examples were replaced with very thin ion exchange membranes.

Example 7

A 100% current efficient ASRS suppressor device was assembled followingexample 1 in U.S. Pat. No. 6,328,885. The device was operated as anelectrolytic ion transfer suppressor/detector 62 of the presentinvention as illustrated in FIG. 3. The ion chromatography separationwas pursued at 21 mM NaOH at 1.2 ml/min flow rate using a proprietarycolumn from Dionex corporation. A standard anion mixture containing fiveanions was injected and the suppressor was operated with 40 mA constantcurrent conditions. The voltage across the suppressor was monitoredusing an UI20 interface from Dionex Corporation. The voltage trace wasinverted for comparative purposes. A conductivity cell was used postsuppressor to monitor the ions. FIG. 16A shows the separation of the 5anions in the conductivity trace. FIG. 16B shows a representative traceof the voltage across the suppressor and shows all five peaks. Anegative dip was observed for the water dip and was significant sincethe resistance of the device increased significantly and the voltageincreased due to the transition of the water dip. The loss of resolutionfor the early elutors stems from this water dip. Overall excellentdetection is feasible by the method as evident from the latter peaks.

Example 8

An EGC KOH cartridge that is commercially available from DionexCorporation was used in this example as an electrolytic ion transferdetector 62 of the present invention. The setup was similar to FIG. 2with the exception that due to the higher delay volume in the EGCcartridge the device 62 was plumbed after the optional conductivitydetector 66. The column used was an IonPac AS11 column from DionexCorporation that was operated with 21 mM sodium hydroxide eluent at 1.2ml/min. In this configuration the voltage across the EGC cartridge wasmonitored using an UI20 interface but without applying any current. Anytransient change in the potential across the EGC cartridge wasindicative of an analyte transition through the sample flow channel ofthe device. The experimental results are shown in FIG. 17. Trace A showsthe EGC voltage trace and trace B shows the conductivity trace. A smallnegative dip after each peak is indicative of a small leakage across theEGC membrane interface causing a small increase in the background. Allfive anions were detected by the device of the present invention.

1. A chromatography system including apparatus for detecting current orpotential generated by ionic species in a sample solution containingsuch ions, said chromatography system comprising: (a) an electrolyticion transfer device including (1) a sample flow-through channel havingan inlet and an outlet, (2) a first charged barrier disposed along saidsample flow-through channel in fluid contact therewith, said firstcharged barrier being capable of passing ions of one charge, positive ornegative, and of blocking bulk liquid flow, (3) a first chamber disposedon the opposite side of said first charged barrier from said sampleflow-through channel, and (4) first and second electrodes in electricalcommunication with said first chamber and said sample flow-throughchannel, respectively; (b) an electrical signal detector in electricalcommunication with said first and second electrodes; (c) achromatography column having an inlet and an outlet, said chromatographycolumn outlet being upstream of and in fluid communication with said iontransfer device sample flow-through channel; and (d) an electrolyticsuppressor having a suppressor sample channel having an inlet and anoutlet, separated from a regenerant channel by a suppressor chargedbarrier capable of passing ions of one charge, positive or negative, andof blocking bulk liquid flow, said suppressor sample channel inlet beingdownstream of and in fluid communication with said chromatography columnoutlet and said suppressor sample channel outlet being upstream of andin fluid communication with said ion transfer device sample flow-throughchannel.
 2. The apparatus of claim 1 in which said first charged barriercomprises an ion exchange bead having exchangeable ions.
 3. Theapparatus of claim 1 in which said first charged barrier comprises anion exchange membrane having exchangeable ions.
 4. The apparatus ofclaim 1 in which said electrical signal detector comprises a currentmeter.
 5. The apparatus of claim 4 further comprising: (5) a secondcharged barrier along said flow-through channel in fluid communicationtherewith spaced from said first charged barrier and capable of passingions of one charge, positive or negative, and (6) a second chamberdisposed on the opposite side of said second charged barrier from saidsample flow-through channel.
 6. The apparatus of claim 5 in which theexchangeable ions of said first charged barrier are of opposite chargeto the exchangeable ions of said second charged barrier.
 7. Theapparatus of claim 5 in which the exchangeable ions of said firstbarrier are of the same charge as the exchangeable ions of said secondbarrier.
 8. The apparatus of claim 1 in which said first chambercomprises a flow-through ion receiving flow channel having an inlet andan outlet, said apparatus further comprising: (e) a recycle conduitdisposed between said sample flow-through channel outlet and said ionreceiving flow channel inlet.
 9. Apparatus for detecting ions in asample solution containing such ions, said apparatus comprising: (a) anelectrolytic ion transfer device including (1) a sample flow-throughchannel, (2) a first charged barrier disposed along said sampleflow-through channel in fluid contact therewith, said first chargedbarrier being capable of passing ions of one charge, positive ornegative, and of blocking bulk liquid flow, (3) a first chamber disposedon the opposite side of said first charged barrier from said sampleflow-through channel, and (4) first and second electrodes in electricalcommunication with said first chamber and said sample flow-throughchannel, respectively; and (b) an electrolytic electrolyte generatordownstream from said electrolytic ion transfer device comprising: (1) afirst electrolyte source reservoir, (2) a first electrolyte generationchamber, (3) a first electrolyte charged barrier capable of passing ionsof one charge, positive or negative, and of blocking bulk liquid flow,disposed between said first electrolyte source reservoir and said firstelectrolyte generation chamber, and (4) third and fourth electrodes inelectrical communication with said first and second electrodes,respectively, and with said first electrode source reservoir and saidelectrolyte generation chamber, respectively, (c) a detector for saidelectrolyte generated in said electrolyte generation chamber in fluidcommunication therewith; and (d) a sample injector upstream of saidsample flowthrough channel.
 10. The apparatus of claim 9 in which saidelectrolytic generator device further comprises (5) a second electrolytegenerator charged barrier along said flow-through channel in fluidcommunication therewith spaced from said first charged barrier capableof passing ions of one charge, positive or negative, and (6) a secondchamber disposed on the opposite side of said second charged barrierfrom said sample flow-through channel.
 11. The apparatus of claim 10 inwhich the exchangeable ions of said first electrolyte generator chargedbarrier are of opposite charge to the exchangeable ions of said secondelectrolyte generator charged barrier.
 12. The apparatus of claim 10 inwhich the exchangeable ions of said first electrolyte generator chargedbarrier are of the same charge as the exchangeable ions of said secondelectrolyte generator barrier.
 13. The apparatus of claim 10 in whichsaid first and second electrolyte generator charged barriers compriseion exchange beads having exchangeable ions of opposite charge to eachother.
 14. The apparatus of claim 10 in which said first and secondelectrolyte generator charged barriers comprise ion exchange membraneshaving exchangeable ions of opposite charge to each other.
 15. Theapparatus of claim 9 in which said electrolyte generator furthercomprises (5) a second electrolyte source reservoir, (6) a secondelectrolyte generation chamber, and (7) a third charged barrier capableof passing ions of one charge, positive or negative, and of blockingbulk liquid flow, disposed between said second electrolyte sourcereservoir and said second electrolyte generation chamber.
 16. A methodfor detecting current or potential generated by ions in a samplesolution containing such ions, said method comprising: (a) providing anelectrolytic ion transfer device including a sample flow-throughchannel, a first charged barrier capable of passing ions of one charge,positive or negative, and of blocking bulk liquid flow disposed alongsaid sample channel in fluid contact therewith, and a first ionreceiving chamber disposed on the opposite side of said first barrierfrom said sample flow through channel, (b) flowing an aqueous samplestream including sample ionic species through said sample channel toexit as a sample channel effluent, (c) passing an electric currentbetween first and second electrodes in electric communication with saidsample stream in said sample channel and aqueous liquid in said ionreceiving chamber, respectively, (d) transporting at least a portion ofthe sample stream ions across said first charged barrier into aqueoussolution in said first ion receiving chamber under the influence of saidelectric current, and, (e) detecting an electrical signal produced bycurrent flowing between said first and second electrodes.
 17. The methodof claim 16 in which said ion transfer device further comprises a secondcharged barrier with exchangeable ions capable of passing ions of onecharge, positive or negative, disposed along said sample channel influid contact therewith said method further comprising: (f) transportingions in said aqueous sample stream across said second barrier intoaqueous solution in a second ion receiving chamber.
 18. The method ofclaim 16 in which said first charged barrier comprises an ion exchangebead having exchangeable ions.
 19. The method of claim 16 in which saidfirst charged barrier comprises an ion exchange membrane havingexchangeable ions.
 20. The method of claim 16 further comprising: (f)chromatographically separating sample ionic species in an eluent streamof one charge, positive or negative, to produce a chromatographyeffluent, and (g) flowing said chromatography effluent through saidsample flow-through channel.
 21. The apparatus of claim 20 furthercomprising: (h) between steps (f) and (g), flowing said chromatographyeffluent through a suppressor to suppress said eluent to exit as asuppressor effluent stream, and flowing said suppressor effluent streamthrough said ion transfer device sample flow channel.
 22. The method ofclaim 16 in which said first ion receiving flow channel includes aninlet and an outlet, said method further comprising recycling saidsample channel effluent to said first ion receiving flow channel inlet.23. The method of claim 20 in which said electrolyte generator furthercomprises a second electrolyte source reservoir separated from saidfirst electrolyte generation chamber by a third charged barrier, saidpotential passing between said third and fourth electrodes causing ionsto be transported from said second electrolyte source reservoir to saidaqueous solution in said first electrode generation chamber.
 24. Themethod of claim 20 further comprising: (i) flowing the aqueous samplestream from said sample flow channel to said electrolyte generationchamber.
 25. Apparatus for detecting analyte in a sample solutioncontaining said analyte, said apparatus comprising: (a) a detectorsample flow channel for liquid sample containing analyte, (b) a signaldetector operatively associated with said detector sample flow channelfor detecting analyte in liquid sample therein, said signal detectorgenerating an electrical signal in response to the concentration of saidanalyte, (c) an electrolytic electrolyte generator comprising (1) afirst electrolyte source reservoir, (2) a first electrolyte generationchamber, (3) a first electrolyte charged barrier capable of passing ionsof one charge, positive or negative, and of blocking bulk liquid flow,disposed between said first electrolyte source reservoir and said firstelectrolyte generation chamber, and (4) first and second electrodes inan electrical circuit with electrical communication with said detectorgenerated electric signal, and with said first electrode sourcereservoir and said electrolyte generation chamber, respectively, and (d)an electrolyte detector for said electrolyte generated in saidelectrolyte generation chamber in fluid communication therewith.
 26. Theapparatus of claim 25 in which said electrolytic generator furthercomprises (5) a second electrolyte generator charged barrier along saidfiow-through channel in fluid communication therewith spaced from saidfirst charged barrier capable of passing ions of one charge, positive ornegative, and (6) a second chamber disposed on the opposite side of saidsecond charged barrier from said sample flow-through channel.
 27. Theapparatus of claim 25 in which said detector is selected from the groupconsisting of a conductivity detector, a photomultiplier based detector,diode array detector, and amperometric detector.